It is intended to observe the release of Ca ion from sarcoplasmic reticulum in intact muscle during excitation-contraction coupling. The technique employed will be that the fluorescent chelate probe in which the muscle is treated with chlorotetracycline. This dye fluoresces from binding sites of Ca ion on membrane surfaces and will visualize Ca ion accumulated by the SR. Detailed kinetics of the process will be under investigation. It is intended to isolate T tubule vesicles from skeletal muscle by density gradient centrigugation. The biochemical and physiological functions of the vesicles will be investigated.